1. Field of the Invention
The present invention relates to an improved compound of a bis-type azo dye which presents a black color, dye which comprises the compound, an ink, a jet printing ink which comprises the dyes, and an ink-jet recording method using the ink.
2. Description of the Related Art
Dyes which present a black color are used not only for the purpose of printing character information, but also as a black print dye in color image printing. However, development of dyes which present a neutral black color is often technically difficult. Although researches and development for the dye has been extensively carried out, there are few dyes having satisfactory properties under the existing circumstances.
For this reason, a method has been carried out, wherein plural dyes having various types of hues are mixed to form the black color. The development of dyes which can present high-density and neutral black color by itself is the technical subject which has been presently demanded most strongly.
With the spread of ink jet printers in recent years, black dyes have become more important than before. In the ink jet printers, printing based on character (letter) information is carried out at an extremely high frequency compared with a pictorial printer of another type. Accordingly, there exits a problem that black dyes used by the ink-jet printers must satisfy conditions which are required both in a case in which the dyes are used for a black image portion of image information and in a case in which the dyes are used for a portion of character information.
The above black dyes must satisfy the following required conditions. For example, they must present a high-density and neutral black color, and they must be excellent in adaptability for ink and ink stability. It is also necessary for the dyes to have high image fastness (that is, high resistance against light, heat, atmospheric moisture, chemicals, air, various gases in the atmosphere, water and friction). Further, they must cause a little variation in hues due to a printing medium (paper), and they must have excellent dyeing properties on image receiving paper. They are furthermore required to be easily synthesized, to be available at a low cost, and to do no harm to living creatures.
Although bis-type azo dyes have been proposed as the block dyes, dyes in which partial structures corresponding to A and B in general formulae (I), (II) and (III) according to the present invention are both heterocycles, have not been known with a few exceptions. Publicly known bis-azo type black dyes have problems that they have a low density (resulting from that a molecular extinction coefficient of the dyes, which is a basic physical property value of dyes, is low), does not have a hue of neutral black (the absorption waveform is broad and light in a visible region is uniformly absorbed), and are deteriorated in image fastness.
Further, some of the black dyes may have a structure in which a harmful chrome ion exists in a molecule, which becomes a problem in the safety to living creatures.
The present invention has been devised in order to solve the above-described problems in the conventional techniques and achieve the following objects.
That is, an object of the present invention is to provide an improved compound which presents a high-density and neutral black color having no other color tint and satisfies various conditions required by dyes, ink and jet printing ink, and which is available at a low cost and easily synthesized.
Further, another object of the present invention is to provide improved dye containing the improved compound, which have excellent printing properties and favorable color tone, have a low degree of dependence on paper, cause no blurring, have excellent water resistance and image storability (for example, light resistance, dark heat storability, and ozone resistance), and present a high-density black color, and also provide an ink and a jet printing ink containing the dyes.
Moreover, still another object of the present invention is to provide an ink-jet recording method in which a black image having excellent image properties is provided by using the jet printing ink.
As a result of their investigations into a bis-type azo dye having a heterocyclic structure which is an improved structure conventionally unknown, the present inventors strove to develop an improved compound which exhibits excellent properties as a black dye, a dye containing the compound, an ink, a jet printing ink containing the dyes, and an ink-jet recording method using the jet printing ink, and has completed the present invention.
The means for solving the above-described objects will be described hereinafter.
A first aspect of the present invention is a compound represented by the following general formula (I). 
In the formula, A and B each independently represents a monovalent heterocyclic group bonded to an azo group by a carbon atom of the monovalent heterocyclic group; m and n each independently represents one of 0 and 1; and M represents one of a hydrogen atom and a monovalent positive ion.
A second aspect of the present invention is a compound represented by the following general formula (II). 
In the formula, A and B each independently represents a monovalent heterocyclic group bonded to an azo group by a carbon atom of the monovalent heterocyclic group; m and n each independently represents one of 0 and 1; M represents one of a hydrogen atom and a monovalent positive ion, which A and B are not both 1H-pyrazole-3-yl at the same time.
A third aspect of the present invention is a compound represented the following general formula (III). 
In the formula, A and B each independently represents a monovalent heterocyclic group bonded to an azo group by a carbon atom of the monovalent heterocyclic group; m and n each independently represents one of 0 and 1; and M represents one of a hydrogen atom and a monovalent positive ion.
A further aspects of the present invention are a dye containing at least one of the above compounds, an ink, a jet printing ink containing the dyes, and an ink-jet recording method in which recording is carried out using the ink.